This invention relates to a heat exchanger. It relates in particular to that form of heat exchanger commonly known as a solar absorber, but the principles of the invention are not limited to this application. The discussion and description which follow deal for convenience with a solar absorber, but their extension to other fields is considered to be obvious.
In this specification, the following definitions are used:
Solar Absorber -- A device with an extended surface exposed to, and absorbing, solar radiation. PA0 Primary Fluid -- The fluid contained within the absorber. PA0 Secondary Fluid -- The fluid that is to be heated and used. Normally potable water for a domestic or industrial hot water supply. PA0 Heat exchanger -- The device which removes heat from the primary fluid and transmits it to the secondary fluid. PA0 Solar Collector -- The complete assembly of weatherproof box, glass cover, back insulation, and solar absorber. Typified by the conventional "flat plate solar collector".
In many parts of the world the sun is a source of heat, and in particular, is a potential source of heat for domestic hot water. It is reliable and cheap in running costs. Many designs for solar absorbers have been produced but most of them are high in capital cost. In general, a solar absorber consists of a receiver of radiant energy, and a means of transferring the heat so collected to the body, commonly water, which is required to be heated. The traditional absorber consists of a blackened surface of a material which is a thermal conductor preferably safeguarded against loss by re-radiation, convection, or conduction and which when exposed to the sun's rays is raised in temperature to a useful extent. The receiver of radiation is almost necessarily a sheet and the heat is tranferred from it by attaching water pipes. The materials and the length of the conduction path from the sheet to the inner surface of a pipe should be as short as practical. The normal method of attaching pipes to a sheet of metal is by soldering, which is an expensive process. The material most commonly used for domestic hot water piping is copper, since there are corrosion problems if the material is not compatible with the material used for the domestic hot water storage tank; copper, is, at present, an expensive material. The manufacture of a solar heat absorber with blackened sheet with an array of copper pipes soldered or brazed to its surface, is technically satisfactory but expensive both in material and labour.